The subject of communications really begins with the situation shown in Figure1. Here is an entity called the Source and one called the User- located remotely from the Source. The Source generates Information and the User desires to learn what this Information is.
Fig.1 SITUATION FOR COMMUNICATION
The question then arises as to how to send the binary data stream from Source to User. A Transmission Medium is employed to transport the Information from Source to User. What is a Transmission Medium? A Transmission Medium is some physical entity. It is located between the Source and the User and it is accessible to both. The Transmission Medium has a set of properties described by physical parameters. The set of properties exists in a quiescent state. However, at least one of these properties can be stressed or disturbed at the Source end. This is accomplished by somehow imparting energy in order to stress the property. This disturbance does not stay still, but affects the parts of the Transmission Medium around it. This disturbance then travels from the Source end to the User end. Consequently, energy imparted in creating the disturbance is thereby transferred from the Source end to the User end. Finally, this disturbance or stressed property can be sensed at the user end.